Elastomers are conventionally reinforced with particulate reinforcing fillers such as, for example, carbon black and sometimes precipitated silica.
It is sometimes difficult to obtain an adequate, homogeneous dispersion of the reinforcing filler, particularly silica, in the rubber composition, by conventionally blending the rubber and filler under high shear conditions.
Accordingly, however, an adequate, homogeneous, dispersion of the reinforcing filler particles within the rubber composition is sometimes desired.
In one aspect, it has heretofore been proposed to create a dispersion of silica in polysiloxane polymers such as poly(dimethylsiloxane), or (PDMS), elastomer(s) by in-situ formation of silica from a base-catalyzed sol-gel conversion of tetraethoxysilane (TEOS). For example see "Precipitation of Silica-Titania Mixed-Oxide Fillers Into Poly(dimethylsiloxane) Networks" by J. Wen and J. Mark; Rubber Chem and Tech, (1994), volume 67, No.5, (pages 806-819).
A process of preparing rubber products has been suggested by mixing the TEOS with a solution of unvulcanized rubber in an organic solvent and subjecting it to a sol-gel condensation reaction to provide a finely powdered silica. For example, see Japanese patent application publication 93/02152.
Further, a composition has been suggested as comprising a base rubber and globular silica made by a sol-gel method and having an average particle diameter of 10-30 microns and specific surface area of 400-700 square meters per gram. The composition is suggested for use in a flap of a tire. For example, see Japanese patent application publication 6145429.
Also, a tread rubber composition has been proposed as a composition of a base rubber and spherical silica prepared by a sol-gel transformation. For example, see Japanese patent application publication 6116440 and corresponding Japanese patent publication 2591569.
Further, an in-situ formation of silica from a sol gel reaction of TEOS in an organic solution of styrene/butadiene rubber, onto which a bis(3-triethoxysilylpropyl) tetrasulfide has been previously grafted to form triethoxysilyl groups, has been reported. ("The Effect of Bis(3-triethoxysilylpropyl) Tetrasulfide on Silica Reinforcement of Styrene-Butadiene Rubber" by Hashim, et al, in Rubber Chem & Tech, 1998, Volume 71, pages 289-299).
In the description of this invention, the term "phr" where used herein, and according to conventional practice, refers to "parts of a respective material per 100 parts by weight of rubber, or elastomer".
In the description of this invention, the terms "rubber" and "elastomer" if used herein, may be used interchangeably, unless otherwise prescribed. The terms "rubber composition", "compounded rubber" and "rubber compound", if used herein, are used interchangeably to refer to "rubber which has been blended or mixed with various ingredients and materials" and such terms are well known to those having skill in the rubber mixing or rubber compounding art.